Analysts at the Horseracing Forensic Laboratory worked through the night to process the samples using enhanced detection methods to identify sophisticated performance-enhancing drugs such as EPO.

Conducted exactly a fortnight before the prestigious Cheltenham Festival, the raids can be seen as a high-risk public relations exercise aimed at rebuffing recent damaging but unsubstantiated claims by Lambourn trainer Charlie Mann that EPO was being used on racecourses "every day".

Despite the clean bill of health, the move has drawn criticism from two of the trainers targeted.

Eleven-times champion jumps trainer Martin Pipe claims the Jockey Club has "not done racing any good at all" and "made no friends down here" for disrupting his yard.

Fellow handler Paul Nicholls said: "They turned up like the bloody mafia yesterday. Who do they think they are?"